The substantial weight of the fifth-wheel travel trailer requires proper mounting of the hitch assembly relative to the axles of the towing vehicle. Where the typical pick-up truck is employed as the towing vehicle, the fifth-wheel hitch is secured in the bed of the truck above and slightly in front of the rear axle. It is desirable that the mounting not be located too far forward of the rear axle so as to avoid unnecessary bending moments about the axle. It is also desirable not to mount the hitch rearward of the axle, otherwise the towing vehicle will tend to rear off its front wheels resulting in loss of steering control.
Where a long-bed truck is employed as the towing vehicle, relatively few difficulties are encountered in the proper mounting of a fifth wheel hitch. Recently, though, the popularity of the short-bed pick-up truck has grown. With such short-bed trucks there is a decreased distance between the rear axle of the truck and the cab. In such cases, and so as to provide adequate clearance between the forward portion of the trailer and the cab during turning operations, the hitch may be mounted rearward in the bed, behind the rear axle. However, as noted above, this creates an undesirable and potentially dangerous towing configuration.
U.S. Pat. No. 6,308,977 to Pulliam et al. teaches a self-adjusting fifth wheel hitch assembly which allows fifth wheel trailers to be towed using short bed pickup trucks, which prevents contact between the trailer and the truck during turning operations and which provides for the proper weight distribution, relative to the rear axle, during normal longitudinal movement of the truck and trailer.
The apparatus of Pulliam et al. includes a first hitch member on the trailer and a second hitch member on the towing vehicle. The hitch member on the towing vehicle is mounted on a sliding mount extending across the rear axle of the vehicle. A linkage is responsive to pivoting between the trailer and towing vehicle to move the hitch on the towing vehicle toward the rear of the vehicle when turning is effected and to move the hitch on the towing vehicle just forward of the rear axle during normal longitudinal movement of the truck and trailer.
However, design of Pulliam et al, is complex, has numerous moving and linked mechanical parts and has multiple hitch members. Many of these mechanical parts responsible for the self-adjustment and pivoting aspects are also subject to the towing force exerted by the truck onto the trailer. This places additional stress on these mechanical components.
What is needed is a self-adjusting fifth wheel hitch which is simple in design and does not have the above-mentioned disadvantages.